The present invention relates to a vehicle mounted ac generator and, particularly, to a cooling structure of such generator.
FIG. 6 shows an example of a conventional vehicle mounted ac generator in cross section. In FIG. 6, a pulley 2 is fixed on a rotary shaft 1 on which a rotor 3 is also fixed. The rotor 3 includes a rotating magnetic field core 4, a field core 5 having a plurality of pole portions 5a extending equiangularly therefrom in parallel to a rotary axis thereof, a support ring 6 of non-magnetic material affixed to an inner periphery of the pole portions 5a and another field core 7 having a plurality of pole portions 7a extending equiangularly therefrom in parallel to the rotary axis. The pole portions 5a and the pole portions 7a are arranged alternately to each other.
The ac generator further includes a stationary field core 8 arranged with air gaps to the rotating field core 4 and the field core 7, a field coil 9 supported by the core 8, an armature core 10 having slots in which an armature coil 11 is supported, a front bracket 12 for supporting through a front bearing 14 the rotary shaft 1 and the armature core 10, a rear bracket 13 for supporting through a rear bearing 15 the rotary shaft 1, the armature core 10 and the field core 8, a rectifier 16 for converting an ac power induced in the armature coil 11 into a dc power, a voltage regulator 17 responsive to an output voltage of the generator for controlling a field current to regulate a terminal voltage to a predetermined value and a fan 18 fixed on the rotary shaft 1. The front bracket 12 has outlet ports 12a for coolant air and the rear bracket 13 has inlet ports 13a for coolant air.
The rotary shaft 1 is rotated by a vehicle engine through a belt to induce an ac voltage in the armature coil 11, which is regulated by the voltage regulator 17 suitably. A dc power obtained by rectifying the regulated ac voltage is supplied to the field coil 9 and to a load such as a battery.
Cooling air is introduced through the inlet ports 13a of the rear bracket 13 to an interior of the generator by the fan 18 and discharged from the outlet ports 12a of the front bracket 12.
In the conventional generator constructed as above, a cooling capacity of the fan 18 is usually insufficient to cool the armature coil 11, the rectifier 16, the voltage regulator 17 and the field coil 9, satisfactorily. Therefore, it is difficult to increase an output current due to a limitation of thermal durability of these components. Further, due to an insufficient cooling of the field coil 9, the output current tends to decrease.
It may be considered, in order to eliminate these problems, to make the fan 18 larger. In such case, noise problems and mounting problems occur. Since there is a limitation of cooling when the fan 18 is used therefor, it is difficult to increase an output current and it is necessary to design the device by taking a considerable lowering of an output into consideration.